Is it a problem to use triangles in a vehicle mesh for a game?
For models that do not undergo deformation (stretching/squishing/bending), it doesn't matter if your model consists only of quads or not. Some nice things about having topology consisting of similarly sized, nearly regular quadrilaterals is that calculations involving adjacent faces are well-behaved, so you won't expect to get weird artifacts during a render, among other things. But this holds for quads and tris.  In general, it is always best to have a model with similarly sized, regular(ish) faces. It is only when you have a model that will deform that you would like to use quads because that allows you to create rings and loops, which enables smooth deformations.